Conventionally, the method for calibrating vehicle cameras by capturing, for example, road surface patterns and by utilizing the camera-captured pattern images has been known and used for calculating camera position errors and for correcting those errors.
For example, Japanese patent documents JP-A-2005-77107 and JP-A-2007-261463 respectively disclose the method for calibrating the vehicle cameras. The former disclosure is about a technique that displays a reference marker image derived from a reference marker (i.e., a pseudo camera-captured reference image captured by a camera that is assumed to be having default values of external parameters) and allows manual adjustments of external parameters that make an actually-captured reference marker image matching with the pseudo image.
The latter disclosure is about a technique that uses a projector looking down on the vehicle to project a pattern around the vehicle and captures the projected pattern by the vehicle cameras for calculating the relationship between the vehicle cameras and the patterns. The technique further calculates the relationship between the vehicle and the patterns by using a camera that is closely disposed at the position of the projector. The technique uses the two relationships for calculating the relationship between the vehicle and the vehicle cameras.
However, the technique in the former disclosure demands a skill in the manual calibration of the vehicle cameras. More specifically, the vehicle having multiple cameras has to go through complicated calibration procedure, thereby taking longer time for the calibration.
Further, the technique in the latter disclosure requires a projector and a camera disposed at a certain position at an outside of the vehicle, thereby demanding both of a well-prepared environment and an investment for the equipment. The dealership that cannot afford the equipment is thus not able to perform the camera calibration on-site in shops.